Method for reducing and /or avoiding the build-up of wood components

ABSTRACT

The invention relates to a method for avoiding and/or reducing the deposition of volatile and non-volatile wood components in gas-bearing systems, whereby at least one of the volatile wood components, at least partly, condenses in the gas-bearing system and the gas contains at least one compound with a similar condensation profile to the volatile wood component and which at least reduces the deposition of volatile wood components or the reaction products thereof. The invention further relates to a method for reducing and/or avoiding the deposition of wood components on machines and/or equipment components for the production of wood fiber materials from wood chippings, in which the shredding of the wood is achieved in the presence of a compound which forms a film on the surfaces of the above machines and/or equipment components and at least reduces the deposition of volatile wood components and/or the reaction products thereof.

[0001] The present invention relates to a process for avoiding and/or reducing deposits of volatile and non-volatile wood constituents in gas-bearing systems, wherein the volatile wood constituents undergo at least partial condensation in the gas-bearing systems.

[0002] The present invention also relates to a process for reducing and/or avoiding deposits of wood constituents on machines and/or plant components used in the production of wood fiber from wood chips.

[0003] In the treatment of wood, in the production and processing of cellulose, and/or in the production of paper, cardboard or molded fibers, volatile wood constituents frequently are released which then undergo condensation in gas-bearing systems, forming solid deposits therein. For example, such deposits increase the pressure drop in pipings, reduce the separation performance of cyclones optionally present, and block control means, so that the gas pipes must be opened and cleaned using e.g. high-pressure apparatus. Such cleaning is highly cost-intensive, interfering with the respective production process.

[0004] The present invention therefore is based on the object of providing a process that would at least reduce deposits of volatile and/or non-volatile wood constituents in gas-bearing systems.

[0005] According to the invention, said object is accomplished by means of a process for avoiding and/or reducing deposits of volatile and non-volatile wood constituents in gas-bearing systems, wherein at least some of the volatile wood constituents undergo at least partial condensation in the gas-bearing systems, and the gas contains at least one compound which

[0006] has condensation characteristics similar to those of said volatile wood constituents, and

[0007] at least reduces deposits of volatile wood constituents and/or reaction products thereof.

[0008] In the meaning of the invention, volatile wood constituents are all those wood constituents exhibiting a vapor pressure at temperatures above 20° C. Reaction products in the meaning of the invention are any products forming volatile wood constituents upon condensation, e.g. as a result of polymerization.

[0009] Condensed volatile wood constituents and the reaction products thereof frequently form a tacky film on the surfaces of gas-bearing systems and therefore, the deposits generally include non-volatile wood constituents as well, e.g. fine wood particles precipitating from the gas stream and adhering to the tacky films.

[0010] According to the invention, said compound exhibits condensation characteristics similar to those of the wood constituents, i.e., the compound and wood constituents undergo condensation preferably at the same location in the gas-bearing system, preferably forming a film there.

[0011] The compound preferably is a dicarboxylic ester. More preferably, said dicarboxylic ester is a dicarboxylic acid dialkyl and/or diisoalkyl ester of C₂-C₁₂ dicarboxylic acids with C₁-C₁₃ n- and/or isoalkanols, such as di-n-butyl oxalate, di-n-butyl malonate, di-n-butyl succinate, di-n-butyl glutarate, di-n-butyl adipate, di-n-butyl suberate, di-n-butyl sebacate, dimethyl adipate, di-n-propyl adipate, diisopropyl adipate, diisobutyl adipate, di-tert-butyl adipate, diisoamyl adipate, din-hexyl adipate, di(2-ethylbutyl) adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, as well as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, di(2-ethylhexyl) phthalate, and diisodecyl phthalate, as well as the corresponding terephthalic esters and diesters of a Cg dicarboxylic acid (trimethyladipic acid) and of dodecanedicarboxylic acid.

[0012] However, it is particularly preferred that the compound be a di-n-alkyl adipate and/or a diisoalkyl adipate. Most preferably, the compound is di-n-butyl adipate.

[0013] The process according to the invention is suitable in avoiding and reducing deposits of volatile or non-volatile wood constituents in gas-bearing systems of any type. However, the gas-bearing systems preferably are part of:

[0014] a wood processing plant, particularly a plant for producing wood fiber material and/or wood fiber boards,

[0015] a plant for producing cellulose,

[0016] a cellulose-processing plant,

[0017] a paper or cardboard production plant, and/or

[0018] a plant for producing components or articles made of molded fiber.

[0019] More preferably, the gas-bearing system is part of a plant for producing thermomechanical pulp (TMP), or a chip refiner plant such as described in WO 96/41914 which hereby is incorporated by reference and is thus deemed part of the disclosure.

[0020] The gas flowing through the gas-bearing pipings can be any gas, but preferably includes water vapor.

[0021] Preferably, the compound is metered into the gas in gaseous state. However, those skilled in the art will recognize that the compound may also be metered into the gas in liquid state, being transformed to the gaseous state therein. Metering preferably is effected continuously.

[0022] The amount of compound metered depends on the concentration of the volatile wood constituents in the gas and on the gas volume flow. The concentration preferably is 100-5000 ppm, more preferably 200-2000 ppm, with 300-1000 ppm being particularly preferred.

[0023] Preferably, the amount of compound metered into the gas is such that no deposits of volatile or non-volatile compounds and/or reaction products thereof will form on the surfaces of the gas-bearing systems, or compounds already having formed will be removed and/or dissolved. Consequently, metering of the compound preferably is subject to automatic control. Preferably, the pressure drop in the piping of the gas-bearing system and/or the separation efficiency of cyclones present in the gas-bearing system are taken as control parameters. It is also preferred to use the gas volume flow and the concentration of volatile wood constituents in the gas, or the surface deposit as control parameters.

[0024] As a rule, the above-mentioned production processes are performed in the presence of water, the water being at least partially evaporated and therefore, in another preferred embodiment of the process according to the invention, the compound is metered directly into the water. In this event, the compound must also be steam-volatile.

[0025] The present invention is advantageous in that the gas-bearing systems require less frequent cleaning, and the plants therefore have longer operating life. For example, cyclones are no longer clogged by deposits, so that their separation capability is maintained. Deposits already existing are reduced. It is another object of the present invention to provide a process for reducing and/or avoiding deposits of wood constituents on machines and/or plant components used in the production of wood fiber from wood chips (chips).

[0026] According to the invention, said object is accomplished by means of a process for reducing and/or avoiding deposits of wood constituents on machines and/or plant components used in the production of wood fiber materials from wood chips, wherein the wood is defiberized in the presence of at least one compound which:

[0027] forms a film on the surfaces of the machines and/or plant components, and

[0028] at least reduces deposits of volatile wood constituents and/or reaction products thereof.

[0029] Deposits in the meaning of the invention are any deposits of wood constituents in gas-bearing and/or water-bearing systems and/or on other components of plants or machinery used in the production of wood fiber materials.

[0030] The compound preferably is a dicarboxylic ester. More preferably, said dicarboxylic ester is a dicarboxylic acid dialkyl and/or diisoalkyl ester of C₂-C₁₂ dicarboxylic acids with C₁-C₁₃ n- and/or isoalkanols, such as di-n-butyl oxalate, di-n-butyl malonate, di-n-butyl succinate, di-n-butyl glutarate, di-n-butyl adipate, di-n-butyl suberate, di-n-butyl sebacate, dimethyl adipate, di-n-propyl adipate, diisopropyl adipate, diisobutyl adipate, di-tert-butyl adipate, diisoamyl adipate, din-hexyl adipate, di(2-ethylbutyl) adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, as well as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, di(2-ethylhexyl) phthalate, and diisodecyl phthalate, as well as the corresponding terephthalic esters and diesters of a Cg dicarboxylic acid (trimethyladipic acid) and of dodecanedicarboxylic acid.

[0031] However, it is particularly preferred that the compound be a di-n-alkyl adipate and/or a diisoalkyl adipate. Most preferably, the compound is di-n-butyl adipate.

[0032] The esters may be employed alone or in combination with water-soluble or water-insoluble solvents as an anhydrous or aqueous solution or as an aqueous dispersion, preferably emulsion. Suitable solvents are n- and isoalkanols, liquid hydrocarbons, acetone, and other well-known solvents. In particular, natural oils or modified natural oils such as rape oil methyl ester are used.

[0033] Non-ionogenic, ionic and amphoteric, particularly non-ionic surfactants are used as emulsifiers in the production of the dispersions.

[0034] For example, suitable non-ionic emulsifiers are oxyalkyl ethers, preferably oxyethylates and/or terminally blocked oxyethylates of fatty alcohols and fatty acids or oils. Alkyl- and/or arylsulfonates, α-olefinsulfonates, α-sulfofatty acid esters, sulfosuccinic acid esters, as well as alkyl sulfates and ether sulfates, as well as carboxymethylated oxyethylates and soaps are suitable as anionic emulsifiers. The preparation of the preferably stable emulsions is well-known. For example, the hydrophobic phase is added to the aqueous phase containing the emulsifier and dispersed with stirring or pump-circulating.

[0035] Preferably, the plant for producing the wood fiber materials has at least one refiner such as known from WO 96/41914 or from WO 96/35016. These patent applications are hereby incorporated by reference and are thus deemed as part of the disclosure.

[0036] The dicarboxylic ester is preferably metered into the refiner together with the clear filtrate. Said metering preferably is effected in a continuous fashion.

[0037] In a preferred embodiment, the dicarboxylic ester concentration in the first refiner is 100-5000 ppm, more preferably 200-2000 ppm, with 300-1000 ppm being particularly preferred.

[0038] The process according to the invention is suitable for any type of machine and plant used in wood defiberizing. However, the machines and/or plants are preferably part of the TMP process or of a process such as described in WO 96/41914.

[0039] Using the present invention, a substantial prolongation of the operating life of machines and plants used in the production of wood fiber materials is achieved. The plants are easier to control, and it is possible to prolong the service life of the refiner milling equipment. It is possible to integrate the process according to the invention in already existing plants. Deposits already present will be reduced by the process of the invention.

[0040] With reference to FIG. 1, the invention will be illustrated below. The explanations are given merely by way of example and do not limit the general idea of the invention.

[0041]FIG. 1 shows a process flow chart for the production of thermomechanical pulp (TMP). Purified chips are fed into the 1^(st) refiner stage and reduced mechanically therein in the presence of clear filtrate and 330 ppm of TALLOFIN® TMP. TALLOFIN® TMP is a product of Stockhausen GmbH & Co. KG, which contains 40 wt.-% of di-n-butyl adipate and 60 wt.-% of a non-ionogenic emulsifier. The TALLOFIN® TMP is metered into the clear filtrate before the latter flows into the refiner. The exceedingly high energy input (up to 22 MW) gives rise to temperatures of more than 200° C. and pressures of 2-3 bars in the refiner, so that a considerable portion of the water undergoes evaporation in the refiner. The steam is removed from the refiner through steam pipings and fed into a heat recovery. In addition to volatile and non-volatile wood constituents, the steam also contains a certain percentage of di-n-butyl adipate, so that the steam pipings, the cyclones and control elements in the steam pipings show no or merely minor deposits. Also, no or massively reduced deposits of wood constituents are formed in the refiner itself, so that the refiner requires less frequent cleaning and the service life of the milling equipment is increased.

[0042] Following defiberization in the first refiner, the wood fibers are reduced mechanically in the 2^(nd) refiner stage once more, before they are subjected to further treatment well-known to those skilled in the art. In the 2^(nd) refiner stage as well, huge amounts of steam are formed which is fed into a heat recovery. Again, in addition to volatile and non-volatile wood constituents, the steam also contains a certain percentage of di-n-butyl adipate, so that the steam pipings, the cyclones and control elements in the steam pipings show no or merely minor deposits. Again, no or massively reduced deposits of wood constituents are formed in this refiner itself, so that it requires less frequent cleaning and the service life of the milling equipment is increased. 

1. A process for avoiding and/or reducing deposits of volatile and non-volatile wood constituents in gas-bearing systems, wherein volatile wood constituents undergo at least partial condensation in the gas-bearing systems, characterized in that the gas contains at least one compound which has condensation characteristics similar to those of said volatile wood constituents, and at least reduces deposits of volatile wood constituents and/or reaction products thereof.
 2. The process according to claim 1, characterized in that said compound is a dicarboxylic ester.
 3. The process according to claim 2, characterized in that said dicarboxylic ester is a di-n-alkyl adipate and/or a diisoalkyl adipate.
 4. The process according to claim 2, characterized in that said dicarboxylic ester is dibutyl adipate.
 5. The process according to any of claims 1 to 4, characterized in that the gas-bearing system is part of: a wood processing plant, particularly a plant for producing wood fiber material and/or wood fiber boards, a plant for producing cellulose, a cellulose-processing plant, a paper or cardboard production plant, and/or a plant for producing components or articles made of molded fiber.
 6. The process according to any of claims 1 to 5, characterized in that the gas includes steam.
 7. A process for reducing and/or avoiding deposits of wood constituents on machines and/or plant components used in the production of wood fiber materials from wood chips, characterized in that wood is defiberized in the presence of at least one compound which: forms a film on the surfaces of the machines and/or plant components, and at least reduces deposits of volatile wood constituents and/or reaction products thereof.
 8. The process according to claim 7, characterized in that said compound is a dicarboxylic ester.
 9. The process according to claim 8, characterized in that said dicarboxylic ester is a di-n-alkyl adipate and/or a diisoalkyl adipate.
 10. The process according to claim 8, characterized in that said dicarboxylic ester is dibutyl adipate.
 11. The process according to any of claims 7 to 10, characterized in that the machines and/or plant components used in the production of wood fiber materials from wood chips include at least one refiner.
 12. The process according to claim 11, characterized in that the dicarboxylic ester is metered into the first refiner together with the clear filtrate.
 13. The process according to claim 11 or 12, characterized in that the concentration of dicarboxylic ester is 100-5000 ppm, preferably 200-2000 ppm, and more preferably 300-1000 ppm.
 14. The process according to any of claims 7 to 13, characterized in that the machines and/or plant components are components of a plant used in the production of thermomechanical pulp. 